SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) $ in Thousands, customer in Millions	12 Months Ended
	Dec. 31, 2022 USD ($) customer regulatedUtility	Dec. 31, 2020 USD ($)	Mar. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Oct. 01, 2021 USD ($)	Dec. 31, 2019 USD ($)
Summary of Accounting Policies [Line Items]
Number of electric and natural gas customers | customer	4.4
Goodwill	$ 4,522,632	$ 4,446,000		$ 4,477,269
Allowance for uncollectible accounts for late fees and other receivable amounts	486,297	358,900		417,406		$ 224,800
Bill of forgiveness	521,752	264,950		221,008		117,063
Cash equivalents	374,600			66,800
Charitable contributions	8,000	6,400
Energy Relief Fund
Summary of Accounting Policies [Line Items]
Restricted cash, current	20,000
Restricted cash, noncurrent	15,900
Restricted cash				41,500
Electric Transmission
Summary of Accounting Policies [Line Items]
Goodwill	576,800	576,800		576,800
Retail (Non-Hardship), Wholesale, and Other
Summary of Accounting Policies [Line Items]
Allowance for uncollectible accounts for late fees and other receivable amounts	201,900	164,100		191,300		81,500
CL&P
Summary of Accounting Policies [Line Items]
Allowance for uncollectible accounts for late fees and other receivable amounts	$ 225,320	157,400		181,319		97,300
Period of accounts receivable recoverable under financial or medical duress	180 days
Maximum loans receivable outstanding	$ 55,000
Loans transferred receivable current	9,100			10,500
Loans transferred receivable non-current	13,000			8,300
Bill of forgiveness	20,327	99,809		74,788		4,971
Cash equivalents	11,300			55,800
Long term receivable	25,000			25,000
CL&P | Customer Assistance Fund
Summary of Accounting Policies [Line Items]
Bill of forgiveness			$ 10,000
CL&P | Unfavorable Regulatory Action
Summary of Accounting Policies [Line Items]
Customer assistance initiatives					$ 10,000
CL&P | Retail (Non-Hardship), Wholesale, and Other
Summary of Accounting Policies [Line Items]
Allowance for uncollectible accounts for late fees and other receivable amounts	$ 36,400	28,300		36,700		17,200
Yankee Gas Services Company
Summary of Accounting Policies [Line Items]
Period of accounts receivable recoverable under financial or medical duress	90 days
NSTAR Electric
Summary of Accounting Policies [Line Items]
Allowance for uncollectible accounts for late fees and other receivable amounts	$ 94,958	91,600		97,005		75,400
Bill of forgiveness	345,293	17,410		18,179		6,312
Cash equivalents	327,700			700
Long term receivable	5,500			5,500
NSTAR Electric | Cash Infusion From Parent
Summary of Accounting Policies [Line Items]
Cash equivalents	327,000
NSTAR Electric | Retail (Non-Hardship), Wholesale, and Other
Summary of Accounting Policies [Line Items]
Allowance for uncollectible accounts for late fees and other receivable amounts	51,300	51,900		53,700		31,500
PSNH
Summary of Accounting Policies [Line Items]
Allowance for uncollectible accounts for late fees and other receivable amounts	29,236	17,200		24,331		10,500
Bill of forgiveness	36,812	$ 39,555		35,126		$ 36,688
Cash equivalents	100			0
Long term receivable	$ 3,800			3,800
Connecticut, Massachusetts and New Hampshire
Summary of Accounting Policies [Line Items]
Number of regulated utilities | regulatedUtility	12
COVID 19
Summary of Accounting Policies [Line Items]
Allowance for uncollectible accounts for late fees and other receivable amounts	$ 50,900			55,300
COVID 19 | CL&P
Summary of Accounting Policies [Line Items]
Allowance for uncollectible accounts for late fees and other receivable amounts	16,000			23,900
COVID 19 | NSTAR Electric
Summary of Accounting Policies [Line Items]
Allowance for uncollectible accounts for late fees and other receivable amounts	$ 4,100			$ 9,000